I designed this sliding door handle lock for our RV bathroom door handle. It's a standard lever type of handle, but it did not have any sort of locking mechanism. Our family has company over, and it's not always known if someone is using the washroom or not (we keep the door closed regardless if anyone is inside or not due to limited space inside the RV) and the toilet is out of arms reach of the door.  

I figured a little extra security would help avoid accidentally walking in on others, so I designed this sliding latch to secure the handle while you are using the washroom.

I used some strong adhesive tape to secure it to the door, and it has held up great over the time.  It's plenty strong enough so that if someone tries to open the door, it will prevent the handle from turning. 

I used PETG HF, and printed it vertical so that the layer lines are oriented in the correct direction against the force of the handle.

If if was to be accidentally locked with no one in the washroom (It hasn't yet) then it would still be easy enough to force it open.  This is just meant to provide a little security for accidental opening while the washroom is occupied, and it has already saved a few people from being walked in on!